The present invention is a system and method to control the acid content and/or total organic carbon of a feed stream including an acid, water and total organic carbon. The present invention permits on-line prediction of acid and TOC composition in order to adjust acid purge rates or the addition of oxidants used to remove carbon.
The process is particularly important in sulfuric acid processes. The composition of the sulfuric acid recycle stream in a sulfuric acid process is essentially comprised of sulfuric acid, water, and organic carbon (TOC). The latter component is a class of heavy hydrocarbons, a portion of which may become insoluble in the sulfuric acid and deposit in vessels, lines, or on heat exchange surfaces. Unit shutdown and maintenance are required to clean the heat exchanger surfaces in the acid concentration section.
Many petrochemical processes, such as alkylation and alcohol production, involve the partially selective extraction of certain hydrocarbon species from a hydrocarbon mixture, by reacting the mixture with aqueous acid. For example, in isopropanol production, propylene is extracted from a hydrocarbon stream with aqueous sulfuric acid. Extraction occurs due to the formation of organic sulfates. Further processing may include hydrolysis to convert the sulfates to alcohol, dehydrogenation reactions to convert the alcohol to ketone, and regeneration of the sulfuric acid for recycle to the extraction process.
Economic advantages associated with minimizing energy and feed acid consumption, and maximizing operability and product yield may be realized by monitoring and controlling the composition and properties of the streams associated with the various steps in the process. For example, a means to determine the acid strength would permit control of the addition of hydrolysis water, thereby optimizing alcohol production, while minimizing the energy expended to reconcentrate the acid for further use.
Another example is a method to determine the total organic content (TOC) of the process streams. This material includes higher molecular weight hydrocarbons formed in the sulfuric acid process, which becomes insoluble in the process stream and deposits on reactor and pipe walls. A method to quantify the amount of this material could be used to determine the optimum process condition.
The present invention is a spectroscopic method and system to determine the acid strength and total organic carbon (TOC) content of acid process streams. It is accurate, rapid, and precise and may be implemented on-line by the use of a fiber optic probe. The invention may be used to determine the acid strength by the difference between the acid and water and to indicate the TOC levels in the acid.